Alk-1-enyl ether silicates and radiation curable composition containing alk-1-enyl ether silicates

ABSTRACT

Subject invention relates to alk-1-enyl ether silicates having the formula 
     
         [X].sub.4-n Si[OR.sub.1 OCH═CH--R.sub.2 ].sub.n 
    
     wherein 
     X is halogen or --OR wherein R is lower alkyl or a mixture of halogen and OR, a mixture of OR and hydrogen or a mixture of halogen and hydrogen; 
     R 1  contains from 1 to 8 carbon atoms and is alkylene, alkenylene, alkynylene, optionally alkoxylated with up to 20 units of ##STR1## wherein Y is hydrogen or methyl and R 2  is each hydrogen or lower alkyl and n has a value of from 1 to 4. The invention also relates to the process for preparing the above vinyl ether silicates and to their use as chemically resistant coatings.

In one aspect, the invention relates to novel alk-1-enyl ether silicatecompounds and in another aspect to their preparation and use.

BACKGROUND OF THE INVENTION

Certain radiation curable coatings and films such as those formed fromthe acrylates, particularly trimethylol propane triacrylate,trimethacrylate, pentaerythritol triacrylate, and hexanediol diacylateor methacrylate, are in great demand because of their rapid curingproperties. However, these compounds are normally highly viscous liquidsor solids and thus are unsuitable as diluents for other polymericcomponents of a radiation curable formulation. Indeed, such compoundsthemselves require the incorporation of a diluent or solvent for uniformsubstrate coating, control of coating thickness and curing at lowtemperatures. Accordingly, low viscosity monofunctional diluents areusually included in their formulations. While these diluents arereactive, they materially reduce the cross-linked density of thefinished product and consequently lower abrasion resistance and abilityto withstand chemical attack.

Although solvents have been used to reduce viscosity, they aredetrimental in radiation curing due to their volatility which presentsproblems for uniform composition control unless their evaporation priorto radiant exposure is effected. Obviously, such procedure extendsprocessing time and may pose environmental drawbacks.

To some extent, the drawbacks of high viscosity monomers can be reducedby curing at elevated temperatures. However, this alternativesignificantly adds to the cost of the overall operation in theexpenditure of energy, temperature control and loss of more volatilecomponents in the composition or blistering of the coating resultingfrom entrained volatiles.

Since acrylate monomers are not conducive to cationically inducedradiation curing, they require free radical systems which are oxygeninhibited unless effected in an inert atmosphere, generally under ablanket of nitrogen. Although formulation with a photoinitiator whichundergoes bimolecular reaction with a hydrogen donor minimizes theinhibitory effect of air, this benefit is realized at the expense of agreatly reduced cure rate. Also, it is found that polymerization orcuring in free radical systems ceases almost immediately upon removalfrom the source of radiation; thus, the cured product often containssignificant amounts of unpolymerized components. Accordingly, it is anaim of research to develop a multifunctional monomer having thebeneficial properties of multifunctional acrylates but which is amenableto radiation curing at a rapid rate by cationically inducedpolymerization which is not oxygen inhibited and which permits continuedpolymerization after removal from the source of radiation exposure.

A monomer having a functionality greater than 2 which is a low viscosityliquid and which can be polymerized cationically is greatly desiredsince such a monomer would allow greater control of the crosslinkdensity of the cured product.

The inherent deficiencies of the acrylate systems can be partiallyovercome by the use of epoxy resins. Epoxy resins can be polymerized bynormal radiation techniques using cationic photoinitiators such asiodonium, sulfonium and ferrocene salts of hexafluorophosphate,hexafluoroantimonate and hexafluoroarsonate to produce a tack free film.Although in such formulations tack free products are obtained,polymerization of the mixture is incomplete. It is well known that thepolymerization of epoxy resins is extremely slow and requires as much asseveral days to achieve their ultimate physical properties. Thus,thermal post curing is often employed to increase the rate of or tocomplete the polymerization.

Certain allyl compounds also have been used as coatings; however thesemonomers and their oligomers are not readily curable by cationicradiation. Thermal curing is generally required to increase the rate ofpolymerization. While allyl ethers of polyethylene glycols are curableby UV light, they require a free radical initiated reaction whichproceeds at a slow rate, generally over a period of from 2 to 10 hoursin order to reach completion.

Finally, it is noted that the unsubstituted acrylates are sensitizersand skin irritants as well as being carcinogenic, so that specializedsafety precautions must be taken to protect operators from exposure.Although alkoxylation has lessened irritancy of the acrylates, theircarcinogenic properties are not reduced.

Accordingly it is an object of the present invention to overcome theabove described deficiencies by an economical and commercially feasiblecomposition and curing process.

Another object of this invention is to utilize a multifunctionalcross-linking agent which is a liquid and which is more economicallyemployed in an efficient cross-linking process.

Another object is to provide a non-toxic cross linkable homopolymericcompound suitable as a film or a substrate coating which possesses goodadhesion, abrasion resistance and resistance to chemical attack.

Still another object is to provide a more economical process forcross-linking monomeric or polymeric vinyl or epoxy ethers which can beeffected in the presence of air.

Another object is to provide a monomer which is curable at a rapid rateby cationically induced radiation.

These and other objects will become apparent from the followingdescription and disclosure.

THE INVENTION

According to this invention there is provided an alk-1-enyl ethersilicate having the formula

    [X].sub.4-n Si[OR.sub.1 OCH═CH-R.sub.2 ].sub.n

wherein X is halogen, --OR wherein R is lower alkyl, a mixture ofhalogen and --OR, a mixture of --OR and hydrogen or a mixture of halogenand hydrogen;

R₁ contains from 1 to 8 carbon atoms and is alkylene, alkenylene,alkynylene, optionally alkoxylated with up to 20 units of ##STR2##wherein Y is hydrogen or methyl, R₂ is hydrogen or lower alkyl and n hasa value of from 1 to 4.

Of the above compounds, those mixtures wherein X contains --OR andwherein R₂ is hydrogen atoms, are preferred and products wherein n has avalue of at least 2 are most preferred. Mixtures of the alk-1-enyl ethersilicates of the present invention can contain varying amounts of 2 to 4components where n has a value of 1,2,3 and/or 4. Preferred mixtures arethose wherein the tris(vinyloxyalkylene) alkyl orthosilicate is present.

The products of this invention are prepared according to the reactionillustrated by the equation: ##STR3## Suitable examples of silicatereactants include tetrachlorosilane, tetrafluorosilane,tetrabromosilane, tetramethyl orthosilicate, tetrabutyl orthosilicate,tetraethyl orthosilicate, tetrapropylyl orthosilicate, diethylorthosilicate, dipropyl orthosilicate, tributyl orthosilicate, triethylorthosilicate, tribromoethyl orthosilicate, dichlorodiethylorthosilicate.

Representative hydroxy vinyl ethers which are suitably employed in thereaction include hydroxybutyl vinyl ether, hydroxyethyl vinyl ether,hydroxybutyl prop-1-enyl ether, hydroxyethyl but-1-enyl ether,hydroxyhexyl vinyl ether, hydroxyethyl 2-butyl hex-1-enyl ether, hydroxybutenyl vinyl ether, hydroxybutynyl vinyl ether,hydroxybutynyl-prop-1-enyl ether, hydroxypropynyl vinyl ether,hydroxybutyl 3-methylprop-1-enyl ether, the vinyl ether ofdi-hydroxymethyl cyclohexane and alkoxylated vinyl ether derivatives ofthe above having the formula ##STR4## where m has a value of from 1 to20, preferably from 1 to 8 and R₁, Y and R₂ are as defined above.

The mole ratio of silicate to hydroxylated alkenyl ether depends on thenumber of terminal alkenyl groups desired in the product and the numberof halo and or OR groups in the silicate reactant and is as close tostoichiometry as is conveniently maintained; although up to a 10:1excess of silicate reactant over said stoichiometric amount is withinthe scope of this invention.

The reaction is carried out under anhydrous conditions in the presenceof from about 0.01 to about 10 wt. %, preferably from about 0.1 to about5%, of a base catalyst based on the alkenyl ether reactant. Catalystssuch as sodium or potassium metals, sodium or potassium hydroxides,hydrides, alkoxides or salts of the hydroxy alkenyl ether as well astitanium alkoxide are suitably employed. When halogenated silicates areemployed, the addition of a base is required during the reaction toneutralize any hydrogen halide which is generated as by-product.Suitable bases include sodium hydroxide, potassium hydroxide, sodium orpotassium alkoxides, pyridine or basic pyridine derivatives, ammonia andamines such as trimethyl amine, tripropylamine and the like.

The reaction mixture may also be affected in up to 90%, preferably notmore than 50% suitable inert solvent such as toluene benzene, methylethyl ketone, N-methyl pyrrolidone, tetrahydrofuran, ethyl acetate,acetonitrile, and the like. Preferred inert solvents are those having aboiling point below that of the desired product.

Generally, the reaction is carried out at a temperature between about50° and about 200° C. for a period of from about 5 to about 48 hoursunder from ambient pressure up to about 500 psi. Preferred reactionparameters include a temperature of between about 100° and about 120°C., a reaction time of from about 10 to 20 hours and a pressure fromatmospheric to about 50 psi.

High conversion to product is achieved in the present reaction althougha product mixture of mono and poly substituted silicates is usuallyobtained. Individual products can be separated by fractionaldistillation if desired. The crude product is separated from basecatalyst by usual methods such as extraction and filtration, and fromsolvent, by evaporation under reduced pressure.

A major advantage of the present products is that they are rapidlycurable at ambient temperatures by UV and visible light or other sourcesof radiation such as an electron beam, x-ray, laser emissions and thelike. They are also reactive diluents for highly viscous coatingmaterials, such as acrylates, vinyl ethers, epoxides, and non-reactiveresins, etc., to promote rapid curing and strong bonding to substratesurfaces. From about 1 to about 60 wt. %, preferably from about 1 toabout 30 wt. %, of the present alk-1-enyl ether silicates are added tosaid acrylates, epoxides and/or vinyl ethers to improve their curingproperties.

The present products, in admixture or individually, can be applied tovarious substrates including metals, glass, ceramics, wood, paper andplastics and cured thereon to provide a strongly adhesive abrasionresistant surface which is water insoluble and which withstands chemicalattack. Coatings of the present product can be applied up to 5 milthickness by any conventional technique. When the substrate is paper,the present materials can contain a coloring agent and can be applied tothe surface as an ink. These and many other uses of the presentproducts, including use as highly reactive chemical intermediates, willbecome apparent from the foregoing disclosure.

Generally, UV light radiation dosages at room temperature of from about100 to about 1500 millijoules/cm² are effective and dosages of fromabout 200 to about 600 millijoules/cm² are preferred. Equivalent dosagesfor curing are employed when using alternative sources of radiation. Forexample, curing with electron beam radiation can be carried out atbetween about 0.5 and about 20 Mrads, preferably between about 1 andabout 10 Mrads. Specific techniques for radiation curing are well known,thus further amplification is not required. Coating mixtures involvingthe present compounds employ a suitable initiator, such as a freeradical and cationic initiator mixture or a cationic photoinitiatore.g., an iodonium, sulfonium or ferrocene salt or mixtures thereof, amixture of aromatic complex salts in butyrolactone (e.g. FX-512,supplied by Minnesota Mining & Mfg. Co.), an aromatic complex salt ofhexafluorophosphate, hexafluoroantimonate, or hexafluoroarsonate, andhydroxycyclohexyl phenyl ketone (IRGACURE 184, supplied by Ciba-Geigy),2-hydroxy-2-methyl-1-phenyl-1-propan-1-one (DAROCUR 1173),2,2-dichloro-1-(4-phenoxyphenyl)ethanone (SANDORAY 1000) and the like.Other free radical and cationic initiators which are suitably employedin this invention are those described by M. J. M. Abadie, Advantages andDevelopment of Photochemical Initiators, in the European CoatingsJournal 5/1988, pages 350-358. The initiator in the composition ispresent in an amount, between about 0.1 and about 10 wt. %, preferablybetween about 0.5 and about 5 wt. % of which at least 25% is a cationicinitiator.

When the silicate compounds of this invention are used as a diluent in apolymerizable composition containing from about 30 to about 99 wt. %,preferably from about 40 to about 60 wt. %, of a vinyl ether, epoxyether, vinyloxy alkyl urethane or oligomer thereof or bisphenol Aepoxyacrylate oligomer, the composition can be cured at a rapid ratewith an initiator containing between about 25 and 100% of a cationicinitiator; although mixtures of a cationic initiator and from about 20to about 75% of a free radical initiator are also beneficially employedand, in fact, are recommended when the polymerizable compound is anepoxy acrylate monomer or oligomer.

The use of a surfactant which is inert with respect to the alk-1-enylether silicate is also beneficially employed in the composition.Fluorochemical surfactants e.g. a mixture of fluoroaliphatic polymericesters (e.g. FC-430 supplied by Minnesota Mining & Mfg. Co.) in aconcentration of from about 0.05 to about 5 parts/100 parts of resinhave been found to be useful.

Having generally described the invention, reference is now had to theaccompanying examples which illustrate preferred embodiments but whichare not to be construed as limiting to the scope of the invention asmore broadly described above and in the appended claims.

EXAMPLE I

A one liter round bottomed flask, equipped with a magnetic stirrer,thermometer, water condenser and dry ice trap attached to vacuum, wascharged with 438 g. (3.78 moles) of hydroxybutyl vinyl ether, 196 g.(0.94 mole) of tetraethylorothosilicate and 5 g. of KOH pellets. Theflask was heated to 55°-60° C. for 4 hours, during which time 40 g. ofethanol by-product was taken off. The vacuum was then removed andnitrogen gas was introduced. The flask was then heated to 110° C. underambient pressure. After 12 hours an additional 78 g. of ethanolby-product was removed.

A. The crude reaction product (463 g.) was flash distilled. The mainfraction (292 g.) distilling at 100°-200° C. under 3 mm Hg was found tocontain 85% tris (vinyl oxybutyl) ethyl orthosilicate and 15% bis (vinyloxybutyl) ethyl orthosilicate.

B. A separate 50 g. portion of the crude reaction product was flashdistilled at 210° C., 1 mm Hg. Analysis of 47 g. of the clear, colorlessdistillate was identified as 81.2% tris (vinyl oxybutyl) ethylorthosilicate, 15.2% bis (vinyl oxybutyl) diethyl orthosilicate and 0.8%tetra (vinyl oxybutyl) orthosilicate.

EXAMPLE II

A 3-necked 100 ml round bottomed flask, equipped with a magneticstirrer, vertical water condenser connected to vacuum via a trap andnitrogen gas inlet was charged with 25 g. of the above main fraction(Example IA), 40 g. of hydroxybutyl vinyl ether and 0.5 g. of KOH. Theflask was heated to 100° C. under a blanket of nitrogen for a period of5 hours after which the mixture was flash distilled, unreacted materialremoved at 100° C. under 3 mm Hg and the remaining distillate collected.The collected distillate was found to be a mixture of 87% tris (vinyloxybutyl ethyl) orthosilicate and 10% tetra (vinyl oxybutyl ethyl)orthosilicate.

EXAMPLE III

The main fraction of Example I (Part A) was mixed with an equal weightamount of the diglycidyl ether of bisphenol A (EPON-828, Shell), 1 partper hundred parts of resin of a fluorochemical surfactant (FC-430), and4 parts per hundred parts of resin of a cationic photoinitiator FX-512at 50° C. until a homogeneous low viscosity liquid was obtained. Thismixture was then coated on an aluminum substrate at a thickness of 1.2mil. The coated surface was exposed for less than 1 second to 400millijoules/cm² from a mercury vapor lamp. A tack free, film wasproduced. Coating properties reported in the following table weredetermined immediately after UV exposure and after a post cure at 177°C. for 15 minutes.

                  TABLE                                                           ______________________________________                                                             After UV  After                                          Property             Exposure  Post Cure                                      ______________________________________                                        Pencil Hardness (ASTM D 3363)                                                                       <4B      F                                              % Adhesion (ASTM D 3359)                                                                            0        80                                             Double MEK Rubs      39        >100                                           Reverse Impact       --        <10                                            Mandrel Bend (in.) (ASTM D 3111)                                                                   1/4       3/4                                            ______________________________________                                    

EXAMPLE IV

The mixture described in Example III was coated on a polyester substrateat a thickness of 0.5 mil. The coated surface was exposed to 400millijoules/cm₂ UV light for less than I second and post cured for 2hours at 50° C. Chemical resistance was tested by the covered spot test(ASTM D 1308). No attack was observed after 24 hours exposure to 1% H₂SO₄, 1% NaOH, 10% acetic acid, or distilled water.

EXAMPLE V

The mixture described in Example III was coated on an aluminum panel ata thickness of 0.25 mil. The coated surface was exposed to an electronbeam dosage of 3 Mrads for less than 1 second to produce a tack freefilm. Coating properties reported in the following Table were determinedimmediately after electron beam exposure and after a post cure at 150°C. for 15 minutes.

                  TABLE                                                           ______________________________________                                        Property         After EB Post Cured                                          ______________________________________                                        Pencil Hardness  HB       H                                                   % Adhesion       100      100                                                 MEK Double Rubs   2        18                                                 Mandrel Bend     1/8      1/8                                                 ______________________________________                                    

EXAMPLE VI

The main fraction of Example I part A (25.0 gm) was mixed with thedivinyl ether of triethylene glycol (25.0 gm) a bisphenol A epoxyacrylate oligomer (EBECRYL-3700, Radcure Specialties, 50.0 gm), 2 phr*cationic photoinitiator (FX 512), 2 phr* free radical photoinitiator(IRGACURE-184) and 1 phr* fluorochemical surfactant (FC-430) at 50° C.until a homogeneous low viscosity liquid was obtained. this mixture wasthen coated on a polyester substrate at a thickness of 0.5 mil.

The coated surface was exposed to 400 millijoules/cm² from a mercurylamp for less than 1 second. A tack free coating with the followingproperties was produced.

    ______________________________________                                        Pencil Hardness  2H                                                           Adhesion           100%                                                       Double MEK Rubs  >100                                                         ______________________________________                                    

EXAMPLE VII

The main fraction from Example I part A (6.20 gm) was mixed with thedivinyl ether of triethylene glycol (18.8 gm) and a divinyl etherurethane oligomer (prepared as described in the Degree Thesis of LennartCarlsson, Dept. of Polymer Technology, The Royal Institute ofTechnology, Stockholm Sweden, 1987; 25.0 gm); 4 phr cationicphotoinitiator (FX-512), and 1 phr fluorochemical surfactant (FC-430) at50° C. until a homogeneous low viscosity liquid was obtained. Thismixture was then coated on a aluminum panel (0.25 mil) and exposed to400 millijoules/cm² from a mercury vapor lamp for less than 1 second. Atack free coating with the following properties was produced

    ______________________________________                                        Pencil Hardness   3B                                                          Mandrel Bend     3/16 inch                                                    Double MEK Rubs  11                                                           ______________________________________                                    

What is claimed is:
 1. An alk-1-enyl ether silicate having the formula

    [X].sub.4-n Si[OR.sub.1 OCH═CH-R.sub.2 ].sub.n

wherein X is halogen, --OR wherein R is lower alkyl, a mixture ofhalogen and --OR, a mixture of --OR and hydrogen or a mixture of halogenand hydrogen; R₁ contains from 1 to 8 carbon atoms and is alkylene,alkenylene, alkynylene optionally alkoxylated with up to 20 units of##STR5## wherein Y is hydrogen or methyl; R₂ is hydrogen or lower alkyland n has a value of from 1 to
 4. 2. The alk-1-enyl ether silicate ofclaim 1 wherein X is --OR, R₂ is hydrogen and n has a value of at least2.
 3. The alk-1-enyl ether silicate of claim 1 wherein X is a mixturecontaining --OR and wherein the value n is said mixture is primarily 3.4. The alk-1-enyl ether silicate of claim 1 which is a mixture ofpoly(vinyloxy lower alkyl) orthosilicates.
 5. The silicate of claim 4wherein said mixture contains

    Si[OR.sub.1 OCH═CH-R.sub.2 ].sub.4


6. The mixture of claim 4 which contain (vinyl oxybutyl) ethylorthosilicates.
 7. The mixture of claim 6 which contains tris(vinyloxybutyl) ethyl orthosilicate.
 8. A radiation curable compositioncomprising (a) between about 0.1 and about 5 wt. % of a photoinitiatorcontaining at least 25% cationic photoinitiator; (b) between about 30and about 99 wt. % of a polymerizable vinyl ether, epoxy ether,epoxyacrylate and/or vinyloxy alkyl urethane and (c) between about 1 andabout 60 wt. % of the alk-1-enyl ether silicate of claim
 1. 9. Thecomposition of claim 8 wherein (a) is a mixture of a cationic and a freeradical initiator.
 10. The composition of claim 9 wherein (b) isbisphenol A epoxyacrylate.
 11. The composition of claim 8 wherein (b) isbetween about 40 and about 60 wt. % and (c) is between about 55 andabout 35 wt. % of the composition.
 12. The composition of claim 8wherein X of the alk-1-enyl ether silicate is a mixture containing --ORand wherein the value of n in said mixture is primarily
 3. 13. Thecomposition of claim 8 wherein the photoinitiator is 100% cationicphotoinitiator and the composition contains from about 40 to about 60wt. % of a polymerizable vinyl ether, epoxy ether or vinyloxy alkylurethane.